Reduced temperature coefficient of frequency at filter transition band while retaining pass-band width

ABSTRACT

An electronic filter includes a plurality of series arm acoustic wave resonators electrically connected in series between an input port and an output port, a plurality of parallel arm acoustic wave resonators electrically connected in parallel and electrically connected on first sides between respective ones of the plurality of series arm acoustic wave resonators and electrically connected on second sides to ground, and at least one additional acoustic wave resonator electrically connected in parallel to one of one of the plurality of series arm acoustic wave resonators or one of the plurality of parallel arm acoustic wave resonators and having a temperature coefficient of frequency (TCF) lower than a TCF of the acoustic wave resonator to which it is electrically connected in parallel.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. § 120 as a continuationof U.S. patent application Ser. No. 16/392,826, titled “REDUCEDTEMPERATURE COEFFICIENT OF FREQUENCY AT FILTER TRANSITION BAND WHILERETAINING PASS-BAND WIDTH,” filed Apr. 24, 2019, which claims priorityunder 35 U.S.C. § 119(e) to U.S. Provisional Patent Application Ser. No.62/667,236, titled “TEMPERATURE COEFFICIENT OF FREQUENCY AT FILTERTRANSITION BAND WHILE RETAINING PASS-BAND WIDTH,” filed May 4, 2018,each of which is incorporated by reference herein in its entirety forall purposes.

BACKGROUND

In the field of information communication devices, for example, mobilephones, the bandgap between transmission and reception frequency bandsin new communication standards are becoming narrower while the desire toutilize all available assigned bandwidth is increasing. The bandgapbetween frequency bands used in different standards is also becomingmore narrow. For example, in the Long Term Evolution (LTE) band 7(a.k.a. IMT-E), the transmission channel occupies frequencies between2,500 MHz to 2,570 MHZ, and the reception channel occupies frequenciesbetween 2,620 MHz and 2,690 MHz. There is only a 0.7% fractional bandgapbetween the frequency bands utilized by LTE band 7 and the WiFi band(2,400 MHz to 2,483 MHz). To avoid interference between signals fromdevices operating on such narrowly spaced frequency bands, it isbecoming increasingly important for RF filters utilized in such devicesto define frequency bands with well-defined sharp boundaries that do notmove significantly under different operating conditions, for example, atdifferent temperatures.

SUMMARY

In accordance with an aspect disclosed herein, there is provided anelectronic filter. The electronic filter comprises a plurality of seriesarm acoustic wave resonators electrically connected in series between aninput port and an output port, a plurality of parallel arm acoustic waveresonators electrically connected in parallel and electrically connectedon first sides between respective ones of the plurality of series armacoustic wave resonators and electrically connected on second sides toground, and at least one additional acoustic wave resonator electricallyconnected in parallel to one of one of the plurality of series armacoustic wave resonators or one of the plurality of parallel armacoustic wave resonators and having a temperature coefficient offrequency (TCF) lower than a TCF of the acoustic wave resonator to whichit is electrically connected in parallel.

In some embodiments, the at least one additional acoustic wave resonatoris electrically connected in parallel to one of the plurality of seriesarm acoustic wave resonators and has a resonant frequency above an upperedge of a passband of the filter.

In some embodiments, the at least one additional acoustic wave resonatoris electrically connected in parallel to one of the plurality ofparallel arm acoustic wave resonators and has a resonant frequency lowerthan a lower edge of a passband of the filter.

In some embodiments, the plurality of series arm acoustic waveresonators, the plurality of parallel arm acoustic wave resonators, andthe at least one additional acoustic wave resonator are bulk acousticwave (BAW) resonators.

In some embodiments, the plurality of series arm acoustic waveresonators, the plurality of parallel arm acoustic wave resonators, andthe at least one additional acoustic wave resonator are surface acousticwave (SAW) resonators having interdigital transducer (IDT) electrodesdisposed on a piezoelectric substrate. The IDT electrodes of theplurality of series arm acoustic wave resonators, the plurality ofparallel arm acoustic wave resonators, and the at least one additionalacoustic wave resonator may be covered by silicon dioxide (SiO₂), theIDT electrodes of the at least one additional acoustic wave resonatorbeing covered by a thicker layer of SiO₂ than the IDT electrodes of theplurality of series arm acoustic wave resonators and the IDT electrodesof the plurality of parallel arm acoustic wave resonators. The at leastone additional acoustic wave resonator may include a first additionalacoustic wave resonator electrically connected in parallel to a firstone of the plurality of series arm acoustic wave resonators and a secondadditional acoustic wave resonator electrically connected in parallel toa second one of the plurality of series arm acoustic wave resonators.Each of the first additional acoustic wave resonator and the secondadditional acoustic wave resonator may have a TCF lower than the firstone of the plurality of series arm acoustic wave resonators and thesecond one of the plurality of series arm acoustic wave resonators. Onlyone of the first additional acoustic wave resonator and the secondadditional acoustic wave resonator may have a TCF lower than the firstone of the plurality of series arm acoustic wave resonators and thesecond one of the plurality of series arm acoustic wave resonators.

In some embodiments, the at least one additional acoustic wave resonatorincludes a first additional acoustic wave resonator electricallyconnected in parallel to a first one of the plurality of parallel armacoustic wave resonators and a second additional acoustic wave resonatorelectrically connected in parallel a second one of the plurality ofparallel arm acoustic wave resonators. Each of the first additionalacoustic wave resonator and the second additional acoustic waveresonator may have a TCF lower than the first one of the plurality ofparallel arm acoustic wave resonators and the second one of theplurality of parallel arm acoustic wave resonators. Only one of thefirst additional acoustic wave resonator and the second additionalacoustic wave resonator may have a TCF lower than the first one of theplurality of parallel arm acoustic wave resonators and the second one ofthe plurality of parallel arm acoustic wave resonators.

In some embodiments, the at least one additional acoustic wave resonatoris electrically connected in parallel to one of the plurality of seriesarm acoustic wave resonators and the IDT electrodes of at least one ofthe plurality of series arm acoustic wave resonators are covered by acovered by a thinner layer of SiO₂ than the IDT electrodes of theplurality of parallel arm acoustic wave resonators.

In some embodiments, the at least one additional acoustic wave resonatoris electrically connected in parallel to one of the plurality ofparallel arm acoustic wave resonators and the IDT electrodes of at leastone of the plurality of parallel arm acoustic wave resonators arecovered by a covered by a thinner layer of SiO₂ than the IDT electrodesof the plurality of series arm acoustic wave resonators.

In some embodiments, the filter further comprises a layer of a siliconnitride covering the SiO₂ over each of the IDT electrodes of theplurality of series arm acoustic wave resonators, the IDT electrodes ofthe plurality of parallel arm acoustic wave resonators, and the IDTelectrodes of the at least one additional acoustic wave resonator

In some embodiments, the IDT electrodes of the plurality of series armacoustic wave resonators and the IDT electrodes of the plurality ofparallel arm acoustic wave resonators have a greater pitch than the IDTelectrodes of the at least one additional acoustic wave resonator.

In some embodiments, the filter is a radio frequency filter. The filtermay be included in a fifth-generation radio frequency circuit. Thefilter may be included in an electronic device module. The filter may beincluded in a transmit and receive module. The electronic device modulemay be a radio frequency device module. The filter may be included in anelectronic device.

In accordance with another aspect, there is provided a method of formingan electronic filter. The method comprises forming a plurality of seriesarm acoustic wave resonators electrically connected in series between aninput port and an output port, forming a plurality of parallel armacoustic wave resonators electrically connected in parallel andelectrically connected on first sides between respective ones of theplurality of series arm acoustic wave resonators and electricallyconnected on second sides to ground, and forming at least one additionalacoustic wave resonator electrically connected in parallel to one of oneof the plurality of series arm acoustic wave resonators or one of theplurality of parallel arm acoustic wave resonators and having atemperature coefficient of frequency (TCF) lower than a TCF of theacoustic wave resonator to which it is electrically connected inparallel.

In some embodiments, forming the at least one additional acoustic waveresonator includes electrically connecting the at least one additionalacoustic wave resonator in parallel to one of the plurality of seriesarm acoustic wave resonators and forming the at least one additionalacoustic wave resonator with a resonant frequency below a lower edge ofa passband of the filter.

In some embodiments, forming the at least one additional acoustic waveresonator includes electrically connecting the at least one additionalacoustic wave resonator in parallel to one of the plurality of parallelarm acoustic wave resonators and forming the at least one additionalacoustic wave resonator with a resonant frequency above an upper edge ofa passband of the filter.

In some embodiments, the plurality of series arm acoustic waveresonators, the plurality of parallel arm acoustic wave resonators, andthe at least one additional acoustic wave resonator are surface acousticwave (SAW) resonators having interdigital transducer (IDT) electrodesdisposed on a piezoelectric substrate and the method further comprisesdepositing a film of silicon dioxide on the IDT electrodes of each ofthe plurality of series arm acoustic wave resonators, the plurality ofparallel arm acoustic wave resonators, and the at least one additionalacoustic wave resonator.

In some embodiments, forming the film of silicon dioxide on the IDTelectrodes of the at least one additional acoustic wave resonatorcomprises forming a thicker film of silicon dioxide on the IDTelectrodes of the at least one additional acoustic wave resonator thanthe films of silicon dioxide on the plurality of series arm acousticwave resonators and the plurality of parallel arm acoustic waveresonators.

In some embodiments, the method further comprises forming films ofsilicon dioxide on the plurality of series arm acoustic wave resonatorsthat are thinner than films of silicon dioxide formed on the pluralityof parallel arm acoustic wave resonators.

BRIEF DESCRIPTION OF THE DRAWINGS

Various aspects of at least one embodiment are discussed below withreference to the accompanying figures, which are not intended to bedrawn to scale. The figures are included to provide illustration and afurther understanding of the various aspects and embodiments, and areincorporated in and constitute a part of this specification, but are notintended as a definition of the limits of the invention. In the figures,each identical or nearly identical component that is illustrated invarious figures is represented by a like numeral. For purposes ofclarity, not every component may be labeled in every figure. In thefigures:

FIG. 1A is a schematic view of an electronic filter;

FIG. 1B is a cross-sectional view of a portion of the electronic filterof FIG. 1A;

FIG. 1C is a cross-sectional view of a portion of an alternateembodiment of the electronic filter of FIG. 1A;

FIG. 1D illustrates an effect of temperature coefficient of frequency atthe lower edge of a passband of the filter of FIG. 1A as compared to analternate design;

FIG. 2A is a schematic view of another electronic filter;

FIG. 2B is a cross-sectional view of a portion of the electronic filterof FIG. 2A;

FIG. 2C illustrates an effect of temperature coefficient of frequency atthe upper edge of a passband of the filter of FIG. 2A as compared to analternate design;

FIG. 3 is a schematic view of another electronic filter;

FIG. 4 is a schematic view of another electronic filter;

FIG. 5A is a schematic view of another electronic filter;

FIG. 5B is a cross-sectional view of a portion of the electronic filterof FIG. 5A;

FIG. 6A is a schematic view of another electronic filter;

FIG. 6B is a cross-sectional view of a portion of the electronic filterof FIG. 6A;

FIG. 7A is a schematic view of another electronic filter;

FIG. 7B illustrates a width of the passband of the filter of FIG. 7A ascompared to an alternate design;

FIG. 8 is a schematic view of another electronic filter;

FIG. 9 is a schematic view of another electronic filter;

FIG. 10A is a schematic view of another electronic filter;

FIG. 10B is a cross-sectional view of a portion of the electronic filterof FIG. 10A;

FIG. 11A is a schematic view of another electronic filter;

FIG. 11B is a cross-sectional view of a portion of the electronic filterof FIG. 11A;

FIG. 12 is a block diagram of a front-end module in which any of thefilters disclosed herein may be implemented; and

FIG. 13 is a block diagram of a wireless device in which any of thefilters disclosed herein may be implemented.

DETAILED DESCRIPTION

Aspects and embodiments disclosed herein include filter structures forwireless communication devices, and methods of manufacturing same, thatexhibit frequency passbands with sharp edges that are stable with regardto operating temperature, exhibiting low temperature coefficients offrequency (TCF). Such filters facilitate operation of wireless devicesunder communication standards having narrow bandgaps betweentransmission and reception frequency bands or having operating bandsthat are closely spaced to the operating bands of devices utilizingother standardized frequency bands. Aspects and embodiments disclosedherein exhibit improvement in TCF at the filter transition band withoutsacrificing passband width to realize telecommunications systems withnarrow bandgap between transmission and reception bands and widepassbands. Aspects and embodiments disclosed herein provide improvementsin TCF at both the upper and lower edges of filter passbands. Specificembodiments include ladder filter structures including acoustic waveelements with dielectric coating thicknesses selected to tune the TCF ofthe of the filter passband edges.

Aspects and embodiments disclosed herein include RF filters built on apiezoelectric substrate, for example, LiNbO₃ or LiTaO₃ and exhibiting aladder structure including series and parallel resonators. Theresonators may include surface acoustic wave (SAW) resonators includinginterleaved interdigital transducer (IDT) electrodes that are covered bya dielectric film, for example, SiO₂ or a combination of dielectricfilms, for example SiO₂ and Si₃N₄. The thickness of the dielectric filmor films on different resonators in the filters may differ to provideenhanced TCF of the edges of the filter passbands as compared to similarfilters having common dielectric thicknesses on all resonators. Aspectsand embodiments disclosed herein will be described primarily withreference to SAW resonators, however, the concepts disclosed herein mayequally apply to RF filters including bulk acoustic wave (BAW)resonators.

A first embodiment is illustrated in FIGS. 1A-1D. The filter of FIG. 1Aincludes a plurality of acoustic wave resonators R1, R2, R3A, R3B, R4,R5, R6, R7, R8, R9 disposed on a piezoelectric substrate 105 between aninput port (IN) and an output port (OUT). The piezoelectric substratemay include, for example, LiNbO₃ or LiTaO₃. Resonators R1, R3A, R5, R7,and R9 are connected in series between the input port and output port.Resonators R2, R4, R6, and R8 are connected in parallel betweenresonators R1, R3A, R5, R7, and R9 and ground. An additional seriesresonator R3B is provided in parallel with resonator R3A. Resonator R3Bhas a resonant frequency lower than the lower edge of the passband ofthe filter. Resonator R3B has a lower TCF than the other resonators inthe filter.

Each of the acoustic wave resonators R1, R2, R3A, R3B, R4, R5, R6, R7,R8, and R9 are SAW resonators including IDT electrodes covered by a SiO₂film. The IDT electrodes of each of resonators R1, R2, R3A, R4, R5, R6,R7, R8, and R9 are covered by an SiO₂ film having a first thickness, forexample, a thickness normalized to the IDT electrode pitch h_(SiO2)/λ,of between about 20% and about 40%. As illustrated in FIG. 1B, thenormalized thickness of the SiO₂ film 110 covering the IDT electrodes115 of resonator R3B is different than the normalized thickness of theSiO₂ film covering the IDT electrodes 115 of the other resonators R1,R2, R3A, R4, R5, R6, R7, R8, and R9. The normalized thickness of theSiO₂ film covering the IDT electrodes of resonator R3B may be, forexample, between about 1% to about 25% greater than the normalizedthickness of the SiO₂ film covering the IDT electrodes of the otherresonators R1, R2, R3A, R4, R5, R6, R7, R8, and R9. By describing thenormalized thickness of the SiO₂ film covering the IDT electrodes ofresonator R3B being between about 1% to about 25% greater than thenormalized thickness of the SiO₂ film covering the IDT electrodes of theother resonators R1, R2, R3A, R4, R5, R6, R7, R8, and R9 it is meantthat if the normalized thickness h_(SiO2)/λ, of the SiO₂ film coveringthe IDT electrodes of the other resonators R1, R2, R3A, R4, R5, R6, R7,R8, and R9 is, for example, 20%, the normalized thickness h_(SiO2)/λ, ofthe SiO₂ film covering the IDT electrodes of resonator R3B may bebetween about 21% and about 45%. A thicker SiO₂ film thickness willgenerally result in a lower acoustic velocity of acoustic waves in a SAWresonator. To compensate for the thicker SiO₂ film, the pitch of the IDTelectrodes of resonator R3B may be reduced so that the resonantfrequency of resonator R3B is lower than the lower edge of the passbandof the filter.

In a method of fabrication of the filter of FIG. 1A, as well as theother filters disclosed herein, the SiO₂ film 110 covering the IDTelectrodes of each of the resonators of the filter may be firstdeposited at a constant thickness over each of the resonators, and thenselectively etched to provide the desired different SiO₂ filmthicknesses over the different resonators.

In some embodiments, as illustrated in FIG. 1C, the SiO₂ film 110 may becovered by a film of another dielectric 120 to provide for frequencytrimming and environmental protection. Dielectric film 120 may be, forexample, silicon nitride (Si₃N₄). Dielectric film 120 may have anormalized thickness h_(Si3N4)/λ, of between about 0.2% and about 3%. Insome embodiments, the dielectric film 120 is planarized as illustratedin FIG. 1C. In other embodiments, the upper surface of the dielectricfilm 120 may conform to the contour of the stepped shape of the SiO₂film 110. In other embodiments the dielectric film 120 may include analternative dielectric material, for example, silicon oxynitride(SiO_(x)N_(y)) or a combination of SiO_(x)N_(y) and Si₃N₄ films with theSiO_(x)N_(y) film disposed between the SiO₂ and Si₃N₄ films or above theSi₃N₄ film. It is to be understood that a second dielectric film 120,for example, a Si₃N₄ film may be disposed over the SiO₂ film of any ofthe embodiments disclosed herein. For brevity, this second dielectricfilm 120 is not illustrated in the other disclosed embodiments.

Provision of the thicker SiO₂ film on the IDT electrodes of resonatorR3B than on the remaining resonators in the filter of FIG. 1A improvesthe TCF of the lower edge of the passband of the filter. As illustratedin FIG. 1D, providing a thicker SiO₂ film on the IDT electrodes ofresonator R3B than on the remaining resonators in the filter of FIG. 1reduces a shift in frequency of the lower edge of the passband of thefilter with temperature. The slope of the lower skirt of the passband ofthe filter may also be improved (increased) due to the provision of thethicker SiO₂ film on the IDT electrodes of resonator R3B than on theremaining resonators in the filter.

A second embodiment is illustrated in FIGS. 2A-2C. The filter of FIG. 2Aincludes a plurality of acoustic wave resonators R1, R2, R3, R4A, R4B,R5, R6, R7, R8, and R9 disposed on a piezoelectric substrate 105 betweenan input port (IN) and an output port (OUT). The piezoelectric substratemay include, for example, LiNbO₃ or LiTaO₃. Resonators R1, R3, R5, R7,and R9 are connected in series between the input port and the outputport. Resonators R2, R4A, R6, and R8 are connected in parallel betweenresonators R1, R3, R5, R7, and R9 and ground. An additional parallelresonator R4B is provided in parallel with resonator R4A. Resonator R4Bhas a resonant frequency above an upper edge of the passband of thefilter. Resonator R4B has a lower TCF than the other resonators in thefilter.

Each of the acoustic wave resonators R1, R2, R3, R4A, R4B, R5, R6, R7,R8, and R9 are SAW resonators including IDT electrodes covered by a SiO₂film. The IDT electrodes of each of resonators R1, R2, R3, R4A, R5, R6,R7, R8, and R9 are covered by an SiO₂ film having a first thickness, forexample, a thickness normalized to the IDT electrode pitch h_(SiO2)/λ,of between about 20% and about 40%. As illustrated in FIG. 2B, thenormalized thickness of the SiO₂ film 110 covering the IDT electrodes115 of resonator R4B is different than the normalized thickness of theSiO₂ film covering the IDT electrodes 115 of the other resonators R1,R2, R3, R4A, R5, R6, R7, R8, and R9. The normalized thickness of theSiO₂ film covering the IDT electrodes of resonator R4B may be, forexample, between about 1% and about 25% greater than the normalizedthickness of the SiO₂ film covering the IDT electrodes of the otherresonators R1, R2, R3, R4A, R5, R6, R7, R8, and R9. A thicker SiO₂ filmthickness will generally result in a lower acoustic velocity of acousticwaves in a SAW resonator. To compensate for the thicker SiO₂ film, thepitch of the IDT electrodes of resonator R4B may be reduced so that theresonant frequency of resonator R4B is located between an upper edge ofthe filter passband and the anti-resonance frequency of the seriesresonators R1, R3, R5, R7, and R9.

Provision of the thicker SiO₂ film on the IDT electrodes of resonatorR4B than on the remaining resonators in the filter of FIG. 2A improvesthe TCF of the upper edge of the passband of the filter. As illustratedin FIG. 2C providing a thicker SiO₂ film on the IDT electrodes ofresonator R4B than on the remaining resonators in the filter of FIG. 2Areduces a shift in frequency of the upper edge of the passband of thefilter with temperature. The slope of the upper skirt of the passband ofthe filter may also be improved (increased) due to the provision of thethicker SiO₂ film on the IDT electrodes of resonator R4B than on theremaining resonators in the filter.

A third embodiment is illustrated in FIG. 3. The filter of FIG. 3includes a plurality of acoustic wave resonators R1, R2, R3A, R3B, R4,R5A, R5B, R6, R7, R8, R9 disposed on a piezoelectric substrate 105between an input port (IN) and an output port (OUT). The piezoelectricsubstrate may include, for example, LiNbO₃ or LiTaO₃. Resonators R1,R3A, R5A, R7, and R9 are connected in series between the input port andthe output port. Resonators R2, R4, R6, and R8 are connected in parallelbetween resonators R1, R3A, R5A, R7, and R9 and ground. Two additionalseries resonators R3B and R5B are provided in parallel with resonatorsR3A and R5A, respectively. Resonators R3B and R5B have resonantfrequencies lower than the lower edge of the passband of the filter.Resonators R3B and R5B have lower TCFs than the other resonators in thefilter.

Each of the acoustic wave resonators R1, R2, R3A, R3B, R4, R5A, R5B, R6,R7, R8, and R9 are SAW resonators including IDT electrodes covered by aSiO₂ film. The IDT electrodes of each of resonators R1, R2, R3A, R4,R5A, R6, R7, R8, and R9 are covered by an SiO₂ film having a firstthickness, for example, a thickness normalized to the IDT electrodepitch h_(SiO2)/λ, of between about 20% and about 40%. The normalizedthickness of the SiO₂ film covering the IDT electrodes of resonators R3Band R5B is different than the normalized thickness of the SiO₂ filmcovering the IDT electrodes of the other resonators R1, R2, R3A, R4,R5A, R6, R7, R8, and R9. The normalized thickness of the SiO₂ filmcovering the IDT electrodes of resonators R3B and R5B may be, forexample, between about 1% and about 25% greater than the normalizedthickness of the SiO₂ film covering the IDT electrodes of the otherresonators R1, R2, R3A, R4, R5A, R6, R7, R8, and R9. A thicker SiO₂ filmthickness will generally result in a lower acoustic velocity of acousticwaves in a SAW resonator. To compensate for the thicker SiO₂ film, thepitch of the IDT electrodes of resonators R3B and R5B may be reduced sothat the resonant frequencies of resonators R3B and R5B are lower thanthe lower edge of the passband of the filter.

Provision of the thicker SiO₂ film on the IDT electrodes of resonatorsR3B and R5B than on the remaining resonators in the filter of FIG. 3improves the TCF of the lower edge of the passband of the filter.Providing a thicker SiO₂ film on the IDT electrodes of resonators R3Band R5B than on the remaining resonators in the filter of FIG. 3 reducesa shift in frequency of the lower edge of the passband of the filterwith temperature.

A fourth embodiment is illustrated in FIG. 4. This embodiment is similarto that of FIG. 3 except the SiO₂ film thickness of each of resonatorsR1, R2, R3A, R4, R5A, R5B, R6, R7, R8, and R9 is the same. The SiO₂ filmthickness of resonator R3B may be, for example, between about 1% andabout 25% greater than the normalized thickness of the SiO₂ filmcovering the IDT electrodes of the other resonators R1, R2, R3A, R4,R5A, R5B, R6, R7, R8, and R9. Resonator R3B has a resonant frequencylower than the lower edge of the passband of the filter. Resonator R3Bhas a lower TCF than the other resonators in the filter. The IDTelectrode pitch of resonator R5B may be similar to that of the parallelresonators R2, R4, R6, and R8. The IDT electrode pitch of resonator R3Bmay be decreased relative to that of the parallel resonators R2, R4, R6,and R8 so that resonator R3B has a resonant frequency lower than thelower edge of the passband of the filter.

Provision of the thicker SiO₂ film on the IDT electrodes of resonatorR3B than on the remaining resonators in the filter of FIG. 4 improvesthe TCF of the lower edge of the passband of the filter. Providing athicker SiO₂ film on the IDT electrodes of resonator R3B than on theremaining resonators in the filter of FIG. 4 reduces a shift infrequency of the lower edge of the passband of the filter withtemperature. Further, in the embodiment of FIG. 4, the fly-back athigher temperature generated due to the TCF difference between theparallel-arm resonators and the resonator R3B having greater SiO₂thickness added in parallel to the series-arm resonator can be reduced.As this term is used herein, fly-back refers to a bump or spike or risein the rejection level out-of-band. This level typically rises (getsworse) away from the passband in frequency.

A fifth embodiment is illustrated in FIG. 5A and FIG. 5B. Thisembodiment is similar to the embodiment illustrated in FIG. 3, however,as illustrated in FIG. 5B, the line width of the IDT electrodes 115A ofthe resonators R3B and R5B added in parallel to the series-armresonators R3A and R5A, respectively, is reduced relative to the linewidths of the IDT electrodes 115 of the other resonators, which may besubstantially identical to one another. The line widths of the IDTelectrodes 115A of resonators R3B and R5B are least among all resonatorsforming the filter. The reduced line width of the IDT electrodes 115A ofresonators R3B and R5B may reduce the TCF of the resonators R3B and R5Bmaking it possible to decrease the extent to which the SiO₂ filmthickness of these resonators is increased relative to the otherresonators to achieve equivalent performance to the embodimentillustrated in FIG. 3. The thickness of the SiO₂ film covering the IDTelectrodes of the resonators R3B and R5B may be between about 0% (nodifference) and about 25% greater than the thickness of the SiO₂ filmcovering the IDT electrodes of the other resonators in the filter,depending on how much thinner the IDT electrodes of the resonators R3Band R5B are relative to the IDT electrodes of the other resonators inthe filter. The reduction of IDT electrode line width for the resonatorsR3B and R5B added in parallel to the series-arm resonators R3A and R5Ain the embodiment of FIG. 5A and FIG. 5B may also be applicable to theembodiments illustrated in FIGS. 1A-1D, FIG. 3 and FIG. 4. In otherembodiments, the line widths of the IDT electrodes of only one ofresonators R3B and R5B, for example, resonator R3B only, are reducedrelative to the line widths of the IDT electrodes 115 of the otherresonators, which may be substantially identical to one another.

A sixth embodiment is illustrated in FIG. 6A and FIG. 6B. Thisembodiment may include any of the features of the embodimentsillustrated in FIGS. 1A-1D, FIG. 3, FIG. 4, or FIG. 5A and FIG. 5B.Additionally, the thickness of the SiO₂ film 110A of the seriesresonators R1, R3A, R5A, R7, and R9 are reduced relative to thethicknesses of the SiO₂ films of the remaining resonators. Theresonators R3B and R5B added in parallel to the series-arm resonatorsR3A and R5A may have the thickest SiO₂ films 110C, the parallelresonators R2, R4, R6, and R8 may have intermediate SiO₂ film 110Bthicknesses, and the series resonators R1, R3A, R5A, R7, and R9 may haveSiO₂ film 110A thicknesses reduced relative to that of the parallelresonators R2, R4, R6, and R8 by, for example, about 5% to about 50%.The embodiment illustrated in FIG. 6A and FIG. 6B may provide similarbenefits with regard to reducing a shift in frequency of the lower edgeof the passband of the filter with temperature as the embodimentsillustrated in FIGS. 1A-1D, FIG. 3, FIG. 4, or FIG. 5A and FIG. 5B andmay additionally provide a wider passband. For example, in a similarfilter illustrated in FIG. 7A, the thickness of the SiO₂ films coveringthe IDT electrodes of the series-arm resonators RB1, RB3, RB5 werereduced relative to the thickness of the SiO₂ films covering the IDTelectrodes of the parallel resonators RB2, RB4, RB6, RB8, and theadditional series arm resonator RB7. The passband of the filter of FIG.7A increased as illustrated in FIG. 7B, which includes a curve of thepassband of a filter similar to that of FIG. 7A but where all resonatorshad similar SiO₂ film thicknesses and a curve of the passband of themodified filter of FIG. 7A. It should be appreciated that in variousembodiments that are reflected by FIG. 6A, the line widths of resonatorR3B, and in some examples, of both R3B and R5B may be reduced asdescribed with reference to FIG. 5B.

An eighth embodiment is illustrated in FIG. 8. The filter of FIG. 8includes a plurality of acoustic wave resonators R1, R2, R3, R4A, R4B,R5, R6A, R6B, R7, R8, and R9 disposed on a piezoelectric substrate 105between an input port (IN) and an output port (OUT). The piezoelectricsubstrate may include, for example, LiNbO₃ or LiTaO₃. Resonators R1, R3,R5, R7, and R9 are connected in series between the input port and theoutput port. Resonators R2, R4A, R6A, and R8 are connected in parallelbetween resonators R1, R3, R5, R7, and R9 and ground. Additionalparallel resonators R4B and R6B are provided in parallel with resonatorsR4A and R6A, respectively. Resonators R4B and R6B have resonantfrequencies above the upper edge of the filter passband and below theanti-resonant frequencies of the series resonators R1, R3, R5, R7, andR9. Resonators R4B and R6B have lower TCFs that the other resonators inthe filter.

Each of the acoustic wave resonators R1, R2, R3, R4A, R4B, R5, R6A, R6B,R7, R8, and R9 are SAW resonators including IDT electrodes covered by aSiO₂ film. The IDT electrodes of each of resonators R1, R2, R3, R4A, R5,R6A, R7, R8, and R9 are covered by an SiO₂ film having a firstthickness, for example, a thickness normalized to the IDT electrodepitch h_(SiO2)/λ, of between about 20% and about 40%. The normalizedthickness of the SiO₂ film covering the IDT electrodes of resonators R4Band R6B is different than the normalized thickness of the SiO₂ filmcovering the IDT electrodes of the other resonators R1, R2, R3, R4A, R5,R6A, R7, R8, and R9. The normalized thickness of the SiO₂ film coveringthe IDT electrodes of resonators R4B and R6B may be, for example,between about 1% and about 25% greater than the normalized thickness ofthe SiO₂ film covering the IDT electrodes of the other resonators R1,R2, R3, R4A, R5, R6A, R7, R8, and R9. A thicker SiO₂ film thickness willgenerally result in a lower acoustic velocity of acoustic waves in a SAWresonator. To compensate for the thicker SiO₂ film, the pitch of the IDTelectrodes of resonators R4B and R6B may be reduced so that the resonantfrequency of resonators R4B and R6B are above the upper edge of thepassband of the filter.

Provision of the thicker SiO₂ film on the IDT electrodes of resonatorsR4B and R6B than on the remaining resonators in the filter of FIG. 8improves the TCF of the upper edge of the passband of the filter.Providing a thicker SiO₂ film on the IDT electrodes of resonators R4Band R6B than on the remaining resonators in the filter of FIG. 8 reducesa shift in frequency of the upper edge of the passband of the filterwith temperature.

A ninth embodiment is illustrated in FIG. 9. This embodiment is similarto that of FIG. 8 except the SiO₂ film thickness of each of resonatorsR1, R2, R3, R4A, R5, R6A, R6B, R7, R8, and R9 is the same. The SiO₂ filmthickness of resonator R4B may be, for example, between about 1% andabout 25% greater than the normalized thickness of the SiO₂ filmcovering the IDT electrodes of the other resonators R1, R2, R3, R4A, R5,R6A, R6B, R7, R8, and R9. Resonator R4B has a resonant frequency similarto the resonant frequencies of the serial-arm resonators R1, R3, R5, R7,and R9. Resonator R4B has a TCF lower than the other resonators in thefilter. The IDT electrode pitch of resonator R6B may be similar to thatof the serial-arm resonators R1, R3, R5, R7, and R9. The IDT electrodepitch of resonator R4B may be decreased relative to that of theserial-arm resonators R1, R3, R5, R7, and R9 so that resonator R4B has aresonant frequency above the upper edge of the filter passband and belowthe anti-resonant frequencies of the serial-arm resonators R1, R3, R5,R7, and R9.

Provision of the thicker SiO₂ film on the IDT electrodes of resonatorR4B than on the remaining resonators in the filter of FIG. 9 improvesthe TCF of the upper edge of the passband of the filter. Providing athicker SiO₂ film on the IDT electrodes of resonator R3B than on theremaining resonators in the filter of FIG. 9 reduces a shift infrequency of the upper edge of the passband of the filter withtemperature. Further, in the embodiment of FIG. 9, the fly-back at lowertemperature generated due to the TCF difference between the series-armresonators and the resonator R4B having greater SiO₂ thickness added inparallel to the parallel-arm resonator R4A can be reduced.

A tenth embodiment is illustrated in FIG. 10A and FIG. 10B. Thisembodiment is similar to the embodiment illustrated in FIG. 8, however,as illustrated in FIG. 10B, the line width of the IDT electrodes 115B ofthe resonators R4B and R6B added in parallel to the parallel-armresonators R4A and R6A, respectively, is reduced relative to the IDTline widths of the IDT electrodes 115 of the other resonators, which maybe substantially identical to one another. The line widths of the IDTelectrodes 115B of resonators R4B and R4B are least among all resonatorsforming the filter. The reduced line width of the IDT electrodes 115B ofresonators R4B and R6B may reduce the TCF of the resonators R4B and R6Bmaking it possible to decrease the extent to which the SiO₂ filmthickness of these resonators is increased relative to the otherresonators to achieve equivalent performance to the embodimentillustrated in FIG. 8. The thickness of the SiO₂ film covering the IDTelectrodes of the resonators R4B and R6B may be between about 0% (nodifference) and about 25% greater than the thickness of the SiO₂ filmcovering the IDT electrodes of the other resonators in the filter,depending on how much thinner the IDT electrodes of the resonators R4Band R6B are relative to the IDT electrodes of the other resonators inthe filter. The reduction of IDT electrode line width for the resonatorsR4B and R6B added in parallel to the parallel-arm resonators R4A and R6Ain the embodiment of FIG. 10A and FIG. 10B may also be applicable to theembodiments illustrated in FIGS. 2A-2C, FIG. 8, and FIG. 9.

An eleventh embodiment is illustrated in FIG. 11A and FIG. 11B. Thisembodiment may include any of the features of the embodimentsillustrated in FIGS. 2A-2C, FIG. 8, FIG. 9, or FIG. 10A and FIG. 10B.Additionally, the thickness of the SiO₂ film 110D of the parallelresonators R2, R4A, R6A, and R8 are reduced relative to the thicknessesof the SiO₂ films of the series arm resonators R1, R3, R5, R7, and R9and the parallel arm resonator R6B. The resonator R4B added in parallelto the parallel-arm resonator R4A may have the thickest SiO₂ film 110F,the series arm resonators R1, R3, R5, R7, and R9 and the parallel armresonator R6B may have intermediate SiO₂ film 110E thicknesses, and theparallel resonators R2, R4A, R6A, and R8 may have SiO₂ film 110Dthicknesses reduced relative to that of the of the series arm resonatorsR1, R3, R5, R7, and R9 and the parallel arm resonator R6B by, forexample, between about 5% and about 50%. The embodiment illustrated inFIG. 11A and FIG. 11B may provide similar benefits with regard toreducing a shift in frequency of the upper edge of the passband of thefilter with temperature as the embodiments illustrated in FIGS. 2A-2C,FIG. 8, FIG. 9, or FIG. 10A and FIG. 10B and may additionally provide awider passband.

Filters as illustrated in any of the above referenced embodiments may beused in a wide range of electronic devices.

Referring to FIG. 12, there is illustrated a block diagram of oneexample of a front-end module 200, which may be used in an electronicdevice such as a wireless communications device (e.g., a mobile phone)for example. The front-end module 200 includes an antenna duplexer 210having a common node 212, an input node 214, and an output node 216. Anantenna 310 is connected to the common node 212. The front-end module200 further includes a transmitter circuit 232 connected to the inputnode 214 of the duplexer 210 and a receiver circuit 234 connected to theoutput node 216 of the duplexer 210. The transmitter circuit 232 cangenerate signals for transmission via the antenna 310, and the receivercircuit 234 can receive and process signals received via the antenna310. In some embodiments, the receiver and transmitter circuits areimplemented as separate components, as shown in FIG. 12; however inother embodiments these components may be integrated into a commontransceiver circuit or module. As will be appreciated by those skilledin the art, the front-end module 200 may include other components thatare not illustrated in FIG. 12 including, but not limited to, switches,electromagnetic couplers, amplifiers, processors, and the like.

The antenna duplexer 210 may include one or more transmission filters222 connected between the input node 214 and the common node 212, andone or more reception filters 224 connected between the common node 212and the output node 216. The passband(s) of the transmission filter(s)are different from the passband(s) of the reception filters. Each of thetransmission filter(s) 222 and the reception filter(s) 224 may includean embodiment of a filter as disclosed herein. An inductor or othermatching component 240 may be connected at the common node 212.

In certain examples, the acoustic wave elements used in the transmissionfilter 222 or the reception filter 224 are disposed on a singlepiezoelectric substrate. This structure reduces the effect of changes intemperature upon the frequency responses of the respective filter, inparticular, reducing degradation in the passing or attenuationcharacteristics due to changes in the temperature, because each acousticwave element changes similarly in response to changes in the ambienttemperature. In addition, this arrangement may also allow thetransmission filter 222 or reception filter 224 to have a small size.

FIG. 13 is a block diagram of one example of a wireless device 300including the antenna duplexer 210 shown in FIG. 12. The wireless device300 can be a cellular phone, smart phone, tablet, modem, communicationnetwork or any other portable or non-portable device configured forvoice or data communication. The wireless device 300 can receive andtransmit signals from the antenna 310. The wireless device includes anembodiment of a front-end module 200′ similar to that discussed abovewith reference to FIG. 12. The front-end module 200′ includes theduplexer 210, as discussed above. In the example shown in FIG. 13 thefront-end module 200′ further includes an antenna switch 250, which canbe configured to switch between different frequency bands or modes, suchas transmit and receive modes, for example. In the example illustratedin FIG. 13, the antenna switch 250 is positioned between the duplexer210 and the antenna 310; however, in other examples the duplexer 210 canbe positioned between the antenna switch 250 and the antenna 310. Inother examples the antenna switch 250 and the duplexer 210 can beintegrated into a single component.

The front end module 200′ includes a transceiver 230 that is configuredto generate signals for transmission or to process received signals. Thetransceiver 230 can include the transmitter circuit 232, which can beconnected to the input node 214 of the duplexer 210, and the receivercircuit 234, which can be connected to the output node 216 of theduplexer 210, as shown in the example of FIG. 12.

Signals generated for transmission by the transmitter circuit 232 arereceived by a power amplifier (PA) module 260, which amplifies thegenerated signals from the transceiver 230. The power amplifier module260 can include one or more power amplifiers. The power amplifier module260 can be used to amplify a wide variety of RF or other frequency-bandtransmission signals. For example, the power amplifier module 260 canreceive an enable signal that can be used to pulse the output of thepower amplifier to aid in transmitting a wireless local area network(WLAN) signal or any other suitable pulsed signal. The power amplifiermodule 260 can be configured to amplify any of a variety of types ofsignal, including, for example, a Global System for Mobile (GSM) signal,a code division multiple access (CDMA) signal, a W-CDMA signal, a LongTerm Evolution (LTE) signal, or an EDGE signal. In certain embodiments,the power amplifier module 260 and associated components includingswitches and the like can be fabricated on gallium arsenide (GaAs)substrates using, for example, high-electron mobility transistors(pHEMT) or insulated-gate bipolar transistors (BiFET), or on a Siliconsubstrate using complementary metal-oxide semiconductor (CMOS) fieldeffect transistors.

Still referring to FIG. 13, the front-end module 200′ may furtherinclude a low noise amplifier module 270, which amplifies receivedsignals from the antenna 310 and provides the amplified signals to thereceiver circuit 234 of the transceiver 230.

The wireless device 300 of FIG. 13 further includes a power managementsub-system 320 that is connected to the transceiver 230 and manages thepower for the operation of the wireless device 300. The power managementsystem 320 can also control the operation of a baseband sub-system 330and various other components of the wireless device 300. The powermanagement system 320 can include, or can be connected to, a battery(not shown) that supplies power for the various components of thewireless device 300. The power management system 320 can further includeone or more processors or controllers that can control the transmissionof signals, for example. In one embodiment, the baseband sub-system 330is connected to a user interface 340 to facilitate various input andoutput of voice and/or data provided to and received from the user. Thebaseband sub-system 330 can also be connected to memory 350 that isconfigured to store data and/or instructions to facilitate the operationof the wireless device, and/or to provide storage of information for theuser.

Devices as disclosed herein that include SAW resonators may operate atfrequencies of up to 3 GHz or higher, for example, between 800 MHz and2.5 GHz. Devices as disclosed herein that include BAW resonators mayoperate at frequencies of up to 5 GHz or higher, for example, operatingin frequencies with wavelengths in the range of from one to ten mm.Filters, modules, and devices disclosed herein may be utilized in fifthgeneration (5G) devices or circuits.

Having described above several aspects of at least one embodiment, it isto be appreciated various alterations, modifications, and improvementswill readily occur to those skilled in the art. Such alterations,modifications, and improvements are intended to be part of thisdisclosure and are intended to be within the scope of the invention. Itis to be appreciated that embodiments of the methods and apparatusesdiscussed herein are not limited in application to the details ofconstruction and the arrangement of components set forth in theforegoing description or illustrated in the accompanying drawings. Themethods and apparatuses are capable of implementation in otherembodiments and of being practiced or of being carried out in variousways. Examples of specific implementations are provided herein forillustrative purposes only and are not intended to be limiting. One ormore features of any embodiment disclosed herein may be added to orsubstituted for any one or more features of any other embodiment. Also,the phraseology and terminology used herein is for the purpose ofdescription and should not be regarded as limiting. The use herein of“including,” “comprising,” “having,” “containing,” “involving,” andvariations thereof is meant to encompass the items listed thereafter andequivalents thereof as well as additional items. References to “or” maybe construed as inclusive so that any terms described using “or” mayindicate any of a single, more than one, and all of the described terms.Any references to front and back, left and right, top and bottom, upperand lower, and vertical and horizontal are intended for convenience ofdescription, not to limit the present systems and methods or theircomponents to any one positional or spatial orientation. Accordingly,the foregoing description and drawings are by way of example only.

What is claimed is:
 1. An electronic filter comprising: a plurality ofseries arm acoustic wave resonators electrically connected in seriesbetween an input port and an output port; a plurality of parallel armacoustic wave resonators electrically connected on first sides betweenrespective ones of the plurality of series arm acoustic wave resonatorsand electrically connected on second sides to ground; and at least oneadditional acoustic wave resonator including a first additional acousticwave resonator electrically connected in parallel with a first one ofthe plurality of series arm acoustic wave resonators and a secondadditional acoustic wave resonator electrically connected in parallelwith a second one of the plurality of series arm acoustic waveresonators, at least one of the first and second additional acousticwave resonators having a temperature coefficient of frequency lower thana temperature coefficient of frequency of the acoustic wave resonator towhich it is electrically connected in parallel.
 2. The filter of claim 1wherein the first additional acoustic wave resonator has a resonantfrequency lower than a lower edge of a passband of the filter.
 3. Thefilter of claim 1 wherein the second additional acoustic wave resonatorhas a resonant frequency above an upper edge of a passband of thefilter.
 4. The filter of claim 1 wherein the plurality of series armacoustic wave resonators, the plurality of parallel arm acoustic waveresonators, and the at least one additional acoustic wave resonator arebulk acoustic wave resonators.
 5. The filter of claim 1 wherein theplurality of series arm acoustic wave resonators, the plurality ofparallel arm acoustic wave resonators, and the at least one additionalacoustic wave resonator are surface acoustic wave resonators havinginterdigital transducer electrodes disposed on a piezoelectricsubstrate.
 6. The filter of claim 5 wherein a line width of theinterdigital transducer electrodes of the at least one additionalacoustic wave resonator is smaller than line widths of at least one ofthe interdigital transducer electrodes of the plurality of series armacoustic wave resonators or the interdigital transducer electrodes ofthe plurality of parallel arm acoustic wave resonators.
 7. The filter ofclaim 5 wherein the interdigital transducer electrodes of the pluralityof series arm acoustic wave resonators, the plurality of parallel armacoustic wave resonators, and the at least one additional acoustic waveresonator are covered by silicon dioxide, the interdigital transducerelectrodes of the at least one additional acoustic wave resonator beingcovered by a thicker layer of silicon dioxide than the interdigitaltransducer electrodes of the plurality of series arm acoustic waveresonators and the interdigital transducer electrodes of the pluralityof parallel arm acoustic wave resonators.
 8. The filter of claim 5wherein the interdigital transducer electrodes of at least one of theplurality of series arm acoustic wave resonators are covered by athinner layer of silicon dioxide than the interdigital transducerelectrodes of the plurality of parallel arm acoustic wave resonators. 9.The filter of claim 5 wherein the interdigital transducer electrodes ofat least one of the plurality of parallel arm acoustic wave resonatorsare covered by a covered by a thinner layer of silicon dioxide than theinterdigital transducer electrodes of the plurality of series armacoustic wave resonators.
 10. The filter of claim 5 further comprising alayer of a silicon nitride covering the silicon dioxide over each of theinterdigital transducer electrodes of the plurality of series armacoustic wave resonators, the interdigital transducer electrodes of theplurality of parallel arm acoustic wave resonators, and the interdigitaltransducer electrodes of the at least one additional acoustic waveresonator
 11. The filter of claim 5 wherein the interdigital transducerelectrodes of the plurality of series arm acoustic wave resonators andthe interdigital transducer electrodes of the plurality of parallel armacoustic wave resonators have a greater pitch than the interdigitaltransducer electrodes of the at least one additional acoustic waveresonator.
 12. The filter of claim 1 wherein each of the firstadditional acoustic wave resonator and the second additional acousticwave resonator has a temperature coefficient of frequency lower than thefirst one of the plurality of series arm acoustic wave resonators andthe second one of the plurality of series arm acoustic wave resonators.13. The filter of claim 1 wherein only one of the first additionalacoustic wave resonator and the second additional acoustic waveresonator has a temperature coefficient of frequency lower than thefirst one of the plurality of series arm acoustic wave resonators andthe second one of the plurality of series arm acoustic wave resonators.14. The filter of claim 1 further comprising a third additional acousticwave resonator electrically connected in parallel with a first one ofthe plurality of parallel arm acoustic wave resonators.
 15. The filterof claim 14 wherein each of the first additional acoustic wave resonatorand the third additional acoustic wave resonator has a temperaturecoefficient of frequency lower than the first one of the plurality ofparallel arm acoustic wave resonators.
 16. The filter of claim 14wherein only one of the first additional acoustic wave resonator and thethird additional acoustic wave resonator has a temperature coefficientof frequency lower than the first one of the plurality of parallel armacoustic wave resonators.
 17. The filter of claim 1 included in afifth-generation radio frequency device module.
 18. The filter of claim17 included in an electronic device.
 19. An electronic filtercomprising: a plurality of series arm surface acoustic wave resonatorselectrically connected in series between an input port and an outputport; a plurality of parallel arm surface acoustic wave resonatorselectrically connected on first sides between respective ones of theplurality of series arm acoustic wave resonators and electricallyconnected on second sides to ground; and at least one additional surfaceacoustic wave resonator electrically connected in parallel with one ofone of the plurality of series arm acoustic wave resonators having atemperature coefficient of frequency (TCF) lower than a TCF of theacoustic wave resonator to which it is electrically connected inparallel, the at least one additional surface acoustic wave resonatorhaving interdigital transducer electrodes covered by a covered by athinner layer of SiO₂ than the interdigital transducer electrodes of theplurality of parallel arm acoustic wave resonators.
 20. A method offorming an electronic filter, the method comprising: forming a pluralityof series arm acoustic wave resonators electrically connected in seriesbetween an input port and an output port; forming a plurality ofparallel arm acoustic wave resonators electrically connected on firstsides between respective ones of the plurality of series arm acousticwave resonators and electrically connected on second sides to ground;and forming at least one additional acoustic wave resonator electricallyconnected in parallel with one of one of the plurality of series armacoustic wave resonators, the at least one additional acoustic waveresonator having a temperature coefficient of frequency lower than atemperature coefficient of frequency of the acoustic wave resonator towhich it is electrically connected in parallel and having a resonantfrequency below a lower edge of a passband of the filter.